PROJECT SUMMARY Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) provide a powerful tool in investigating cardiac disease by enabling us to model genetic cardiac conditions in vitro. Those models provide unique insight into the pathophysiology of disease and allow for the screening and evaluation of potential interventions. Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a genetic disease affecting cell-cell adhesion in cardiomyocytes. Arrhythmia associated with ARVC is a major cause of sudden cardiac death in the United States, especially among young, low risk populations. The parent grant, ?ARVD/C Dysfunction in Human Stem Cell-Derived Cardiac Tissue? focuses on using iPSC-CMs derived from ARVC patients to generate engineered heart slices (EHS) to study how structural defects promote arrhythmia in ARVC. While that proposal focuses primarily on the early stages of the disease, when structural changes are not manifest on a macroscopic scale, this project aims to create a late-stage model of ARVC, where fibrosis and fatty infiltrate of myocardial tissue are prominent features. Thus, the Specific Aim of the project is to simulate the late-stage, fibro-fatty disease condition of ARVC by addition of myofibroblasts and adipocytes to ARVC EHS. Phase 1 of the project will be to create a fibrosis-like model of ARVC myocardium that displays characteristic conduction slowing and increased incidence of reentrant arrhythmia by co-culturing hiPSC-CMs with myofibroblasts (fibrosis-producing cells) in EHS. Phase 2 of the project will be to incorporate fatty infiltration into the fibrotic ARVC EHS model by tri-culture of adipocytes (fat-producing cells) with hiPSC-CMs and myofibroblasts and to test for further slowing of conduction and increased susceptibility to arrhythmia.